A related-art automobile steering device is configured as shown in FIG. 19. When rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, the input shaft 3 is rotated, so that right and left tie rods 4, 4 are pushed and pulled to apply a steering angle to front wheels. The steering wheel 1 is supported and fixed to a rear end portion of a steering shaft 5. The steering shaft 5 is rotatably supported to a cylindrical steering column 6 in a state of being axially inserted into the steering column 6. A front end portion of the steering shaft 5 is connected to a rear end portion of an intermediate shaft 8 via a universal joint 7. A front end portion of the intermediate shaft 8 is connected to the input shaft 3 via another universal joint 9. In the specification, a front-rear direction, a left-right direction (width direction) and an upper-lower direction indicate a front-rear direction, a left-right direction (width direction) and an upper-lower direction of a vehicle, unless particularly otherwise mentioned.
In the steering device configured as described above, there has been known a tilt mechanism for adjusting an upper-lower position of the steering wheel 1 and a telescopic mechanism for adjusting a front-rear position of the steering wheel 1 in accordance with a physique and a driving posture of a driver. In order to configure the tilt mechanism, a front end portion of the steering column 6 is supported to a vehicle body 10 so as to be pivotably displaceable about a pivot shaft 11 mounted in the left-right direction. A displacement bracket 12 is fixed to a rear end side portion of the steering column 6 and is supported to a support bracket 13 supported to the vehicle body 10 so as to be displaceable in the upper-lower direction and the front-rear direction. In order to configure the telescopic mechanism, the steering column 6 has a structure where an outer column 14 and an inner column 15 are telescopically combined. The steering shaft 5 has a structure where an outer shaft 16 and an inner shaft 17 are combined to transmit torque and to be telescopic by a spline engagement and the like. In the example of FIG. 19, there is incorporated an electric power steering device configured to reduce a force necessary to operate the steering wheel 1 by using an electric motor 18 as an auxiliary power source.
In case of a manual type except an electric type, the tilt mechanism and the telescopic mechanism are configured to adjust a position of the steering wheel 1 and to fix the steering wheel 1 to an adjusted position based on an operation of an adjustment lever. As the structure of the tilt mechanism or telescopic mechanism of the manual type, various structures have been known and implemented. For example, in case of the structure shown in FIG. 19, the displacement bracket 12 fixed to the outer column 14 is formed with a front-rear long hole 19 which is long in an axial direction of the outer column 14, which is a front-rear position adjustment direction. The support bracket 13 has a pair of support plate parts 20 configured to interpose therebetween the displacement bracket 12 from left and right sides. Upper-lower long holes 21, which are long in the upper-lower direction, are formed at portions of the support plate parts 20 facing each other. The upper-lower long hole 21 has generally a partial arc shape having the pivot shaft 11 as a center. An adjustment rod 22 is inserted into the upper-lower long holes 21 and the front-rear long hole 19. The adjustment rod 22 is provided with a pair of pressing parts configured to interpose therebetween the support plate parts 20 from left and right sides. An expansion and contraction device is configured to expand and contract an interval between the pressing parts based on an operation of the adjustment lever.
When adjusting an upper-lower position or front-rear position of the steering wheel 1, the adjustment lever is rotated in a predetermined direction (a downward direction, generally), thereby expanding the interval between the pressing parts. Accordingly, the frictional force acting between an inner surface of the support plate parts 20 and an outer surface of the displacement bracket 12 is reduced. At this state, the adjustment rod 22 adjusts a position of the steering wheel 1 within a range displaceable in the upper-lower long holes 21 and the front-rear long hole 19. After the adjustment, the adjustment lever is rotated in a reverse direction (an upward direction, generally) to the predetermined direction, thereby contracting the interval between the pressing parts. Accordingly, the frictional force is increased to hold the steering wheel 1 at an adjusted position.
The steering device has a structure which permits the steering wheel 1 to be displaced forwards so as to alleviate the shock load to be applied to the driver when a secondary collision that a driver's body collides with the steering wheel 1 occurs upon collision accident. Specifically, the support bracket 13 is supported to the vehicle body 10 to be separated forwards by the shock caused upon the secondary collision. In the steering device having this structure, when the force of holding the steering wheel 1 at the adjusted position, i.e., the holding force of the outer column 14 to the support bracket 13 is weak, the outer column 14 may be unintentionally moved relative to the support bracket 13 upon the secondary collision. If the outer column 14 is moved, since the manner of the shock to be applied to the support bracket 13 varies, it may be difficult to design a shock absorption mechanism based on the configuration where the support bracket 13 is to be separated from the vehicle body 10.
In the meantime, in order to increase the holding force of the outer column 14 to the support bracket 13 without increasing an adjusting amount or adjusting force of the adjustment lever, it is preferably to increase the number of friction surfaces for securing the holding force. In view of this situation, Patent Document 1 discloses a structure of increasing the number of friction surfaces by overlapping a friction plate supported to the steering column and a friction plate supported to the support bracket in the left-right direction. However, according to the structure disclosed in Patent Document 1, each friction plate is supported to the steering column or the support bracket to be displaceable only in the left-right direction. For this reason, the number of the friction plates necessary to increase the number of the friction surfaces increases. Therefore, as the number of the friction surfaces increases, the size in the left-right direction, the number of components and the weight are respectively increased.